During the past year, the procedures developed previously were used to obtain adenylylcyclase preparations of unprecedented specific activity. Immunoblot analysis of this material using antibodies directed at defined sequences of two different cloned forms of the enzyme indicated that a majority of the enzymatic activity corresponded to a heretofore undescribed isoform. During the course of these studies, it was discovered that preactivation of the bovine brain membranes used as source material for the enzyme with a non-hydrolyzable GTP analog resulted in enhanced physical association between adenylylcyclase and the beta subunit of the stimulatory GTP binding protein, Gs. Manuscripts describing these findings have been completed and will be submitted shortly, and the project has been terminated.